When Who or What IS the subject of the question.
Who wrote this book? What happened? Who called you?
No do/does/did used!
Who broke the vase?
When asking about the object of the verb.
Who did you call? What did you see? Where do you live?
Requires do/does/did
Who did you invite?
| Example / Question | Positive / Short Answer | Negative / Short Answer |
|---|---|---|
| Subject Question: Who called? | Who called you? | Not: Who did call you? |
| Object Question: Who did you call? | Who did you call? | Requires: did + subject + bare V |
| Rule | Base / Standard Form | Applied Form |
|---|---|---|
| No Auxiliary Rule for Subject Questions | When Who/What acts as the Subject in Present or Past Simple, DO NOT use do, does, or did! Conjugate the main verb directly like a statement. | Who lives here? (NOT "Who does live here?") |
Used when the subject of an action is unknown.
Replace Who with a name (e.g., "John called me"). Since John is the Subject, "Who called me?" is a Subject question!